For four months, starting Friday night, drivers on the northbound 405 Freeway will not be able to exit on Sunset Boulevard.

The off-ramp will be closed until Dec. 1 as crews build a longer exit, which officials say will add 60% capacity in one of the Westside's most congested intersections. Crews will also widen the Sunset Bridge over the freeway and an undercrossing.

The new off-ramp will feature two right-hand turn lanes to eastbound Sunset and one left-turn lane to westbound Sunset.

For eastbound Sunset drivers, the recommended detour is the eastbound Wilshire off-ramp.

The construction is part of Metro's ongoing effort to widen the 405 Freeway. Officials say the project is slated for completion in 2014, a year later than expected, and more than $100 million over budget.